Intervertebral implant

ABSTRACT

The intervertebral three-dimensional structure comprises a top side, an underside, a front face, a rear face, and a plurality of boreholes designed to receive affixation elements.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/012,626, filed Jan. 24, 2011, which is a continuation of U.S. patentapplication Ser. No. 12/574,222, filed Oct. 6, 2009, now U.S. Pat. No.7,875,076, which is a continuation of U.S. patent application Ser. No.11/751,757, filed May 22, 2007, now U.S. Pat. No. 7,618,456, which is acontinuation of U.S. patent application Ser. No. 10/923,534, filed Aug.19, 2004, now U.S. Pat. No. 7,232,464, which is a continuation ofInternational Application No. PCT/CH02/00099, filed Feb. 19, 2002. Theentire contents of each of the applications identified above areexpressly incorporated herein by reference thereto.

TECHNICAL FIELD

The present invention relates to an intervertebral implant.

BACKGROUND

Such an intervertebral implant is known from the British patent document2,207,607 A which discloses a horseshoe implant structure having aplurality of cylindrical holes. These holes are fitted with inner,smooth surfaces and comprise only one stop for the heads of the bonescrews to be inserted into them. This design incurs the drawback thatthe inserted affixation screws may be anchored into the bone only bytheir shanks, a rigid connection with the horseshoe shapedintervertebral implant being lacking. As soon as the anchoring of thebone screw in the bone is weakened, the intervertebral implant becomesdisplaceable relative to the screw and the bone screws may then migratewhile endangering the blood vessels. Moreover the loosening of theintervertebral implant may entail pseudoarthrosis.

The above cited state of the art is intended merely to elucidate thebackground of the present invention but it does imply that the citedstate of the art had actually been made public or was publicly known atthe time of this application or at the time of its priority.

SUMMARY

The objective of the present invention is palliation. This inventioncreates an intervertebral implant which is able to rigidly connect tobone affixation means in a manner that even in the event of bonestructure weakening, loosening between the intervertebral implant andthe bone affixation means shall be precluded.

The above problem is solved in the present invention by anintervertebral implant exhibiting the features of claim 1.

The advantages offered by the present invention substantially areattained by the rigid, that is by the firm connection between theintervertebral implant and the longitudinal affixing elements. Basicallytwo different embodiment modes are available to attain said rigidconnection.

In a first embodiment mode, at least one of the boreholes shall beinternally threaded. In this case a matching bone screw fitted with athread head may be rigidly screwed into the implant.

As regards a second embodiment mode, a front plate is mounted at thefront surface of the three dimensional (3D) implant structure so as tobe configured vertically to the horizontal center plane of theintervertebral implant, said boreholes passing through said front plateand receiving the anchored longitudinal affixation elements. Compared tothe state of the art of a two-part implant, wherein a front plate isimplanted in a separate operational step, the above design of thepresent invention offers the advantage that the intervertebral implantshall be implanted in a single step and hence in a simple and quickermanner. The invention offers a further advantage in that theintervertebral implant shall be affixed as frontally to the vertebra aspossible, namely at a place where good bone material may be expected tobe. As a result anterior displacement is restricted without therebyincurring greater danger to the surrounding structures than when using astate of the art intervertebral implant. The load still is being borneby the compressed vertebral implant, not by the front plate or theaffixation screws.

In yet another embodiment mode of the present invention, the front plateis displaceably configured in the 3D implant structure in order that itmay move vertically relative to this 3D implant structure. “Stressshielding” is attained in this manner (namely protection from orneutralization of mechanical stresses), and as a result the end platesmay gradually match the intervertebral implant during the healingprocess.

As regards a further embodiment, the front plate is made of a materialdifferent from that of the 3D implant structure.

As regards a further embodiment of the present invention, at least oneborehole tapers conically towards its underside and as a result a bonescrew fitted with a matching conical head may be rigidly anchored insaid borehole. Preferably the conical borehole exhibits a cone anglesmaller than the resultant angle of friction. Appropriately theborehole's conicity shall be 1:3.75 to 1:20, preferably 1:5 to 1:15.

As regards a further embodiment mode of the present invention, theintervertebral implant side faces shall all be substantially convex.

Appropriately the intervertebral implant's top and/or undersides are notplanar but convex. In this manner better matching to the end plates ofthe adjacent vertebras may be attained.

The boreholes preferably shall not pass through the left and rightintervertebral implant side faces. Preferably again no borehole shallrun through the front surface.

As regards a further preferred embodiment mode of the present invention,at least two boreholes shall be mutually parallel. This featuresfacilitates inserting the vertebral implant during implantation.

As regards another preferred embodiment mode of the present invention,at least two boreholes shall run in mutually divergent manner as seenfrom the front side. As a result the bone screws shall move into avertebral region offering better bone quality than found at thevertebra's center. Appropriately the borehole axes subtend an angle of25 degrees to 70 degrees, preferably 35 degrees to 55 degrees with thehorizontal center plane. This feature offers improved access for screwinsertion.

As regards a further embodiment mode of the present invention, theboreholes shall not cross the horizontal center plane.

Depending on circumstance, two, three, four or even more longitudinalaffixation elements may rigidly connected to the intervertebral implant;appropriately at least one affixation element shall pass through the topside and at least one affixation element shall pass through theintervertebral implant side.

Preferably the longitudinal affixation elements shall be bone screwscomprising a head and a shank, said head preferably being fitted with anexternal thread that matches the inner thread of the intervertebralimplant's borehole. As regards a second appropriate connection,preferably a bone screw shall be used of which the head tapers conicallyin the direction of the shank, the head's conicity corresponding to thatof the intervertebral implant's borehole.

Regarding a further embodiment mode, at least two longitudinalaffixation elements pass through the top side and at least twolongitudinal affixation elements pass through the underside. In thismanner the intervertebral implant is optimally anchored into theadjacent vertebras.

Preferably the screw-shaped longitudinal affixation elements exhibit aself-boring and self tapping external thread. The longitudinalaffixation elements also may be designed as unthreaded cylindrical pinsfitted with a boring tip, preferably in the form of a trocar.

In another embodiment variation, the longitudinal affixation elementsare spiral springs; lastly said longitudinal affixation elements alsomay be designed as single or multi-wing spiral blades.

In a further embodiment mode of the present invention, the longitudinalaffixation element tip may be anchored in the structure of theintervertebral implant, as a result of which the head of thelongitudinal affixation element may be anchored in the adjacentvertebra.

In a further embodiment mode of the present invention, the longitudinalaffixation element head exhibits a widened diameter; also a support diskis provided for said head to rest against the vertebra.

The intervertebral implant may be made of any physiologically compatiblematerial, though appropriately the implant structure shall consist of aphysiologically compatible plastic, preferably an unreinforced plastic.The advantage offered by the invention over the already known,fiber-reinforced plastics used in implantology is that no reinforcingfibers will be bared--an eventuality that would be clinicallydisadvantageous. Appropriately bone screws consisting of non-reinforcedplastic of which the external threads exhibit load bevels of 11 degreesto 14 degrees, preferably 12 degrees to 13 degrees, may be used in suchan implant structure. The relatively small slope of the load bevelimplements high clamping forces, as a result of which radial elongationand danger of cracking of the plastic are reduced. Appropriately thebone screws' external thread exhibits the bones at an angular pitch of 6degrees to 10 degrees, preferably 7 degrees to 9 degrees. Thisparticular angular pitch produces thread self-locking and prevents thebone screw from loosening on its own.

The borehole may be in the form of a metal bush fitted with an innerthread for the purpose of improving anchoring the bone screw in theplastic implant structure. The intervertebral implant also may consistpartly of plastic and, in the borehole zones, of metal. This designoffers improved guidance and anchoring of the bone screw in theintervertebral implant.

As regards a further preferred embodiment mode, the inside boreholewalls are smooth, the thread head of a metallic, longitudinal affixationelement cutting or tapping into said smooth wall.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention and further embodiment modes of it are elucidatedbelow in relation to the partly schematic representation of twoillustrative embodiments.

FIG. 1 is a perspective view including a partial section of theintervertebral implant with inserted bone screws,

FIG. 2 is a front view of the intervertebral implant of FIG. 1,

FIG. 3 is a side view of the intervertebral implant of FIG. 1,

FIG. 4 is a top view of the intervertebral implant of FIG. 1,

FIG. 5 is a front view of the intervertebral implant with a frontinsert, in partial section,

FIG. 6 is a vertical, longitudinal section of the intervertebral implantof FIG. 5, and

FIG. 7 is a horizontal cross-section of the intervertebral implant ofFIG. 5.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The intervertebral implant of FIGS. 1 through 4 consists of a 3Dstructure 10 exhibiting both a convex top side 1 and a convex underside2, the two sides each being designed to rest against the end plates oftwo adjacent vertebras. To attain improved anchoring, the top side 1 andthe underside 2 may be topographically shaped and be fitted withgrooves, ribs or teeth, or their surfaces may be merely roughened.

The 3D implant structure 10 moreover comprises a left side face 3 and aright side face 4, also a front face 5 and a rear face 6. The implantstructure 10 also may be hollow and its outer surface may compriseperforations.

The implant structure 10 comprises a plurality of boreholes 9 passingthrough it and receiving longitudinal affixation elements 20. Preferablyfour such boreholes 9 shall be provided.

At least one of the boreholes 9 is designed in a way that thelongitudinal affixation element 20 received therein may be rigidlyconnected to the intervertebral implant. The boreholes 9 are conical forthat purpose.

Preferably the affixation elements 20 are bone screws having a head 21and a tip 22. The head 21 conically tapers toward the shank 23, theconicity of the head 21 corresponding to the conicity of the borehole 9.Moreover the four boreholes 9 may be fitted with inner threads 11.

As regards the embodiment variation shown in FIGS. 5 through 7, the 3Dstructure 10 is fitted at its front face 5 with a preferably metallicinsert 8 into which the affixation elements 20 may be anchored. Theinsert 8 is mounted in vertically displaceable manner in the 3Dstructure 10.

While the invention has been shown and described herein with referenceto particular embodiments, it is to be understood that the variousadditions, substitutions, or modifications of form, structure,arrangement, proportions, materials, and components and otherwise, usedin the practice and which are particularly adapted to specificenvironments and operative requirements, may be made to the describedembodiments without departing from the spirit and scope of the presentinvention. Accordingly, it should be understood that the embodimentsdisclosed herein are merely illustrative of the principles of theinvention. Various other modifications may be made by those skilled inthe art which will embody the principles of the invention and fallwithin the spirit and the scope thereof

1. A bone stabilizing system for stabilizing first and second vertebraein a spinal column comprising: a plurality of bone screws having athreaded shaft and a head, the shaft having a longitudinal central axis;a three dimensional body configured for insertion between the endplatesof vertebrae, the three dimensional body having an upper surface forabutting the endplate of the first vertebrae, a lower surface forabutting the endplate of the second vertebrae, a front surface, and ahorizontal center plane between the upper and lower surface; and a frontplate having a top surface and a bottom surface, the plate coupleable tothe body such that the bottom surface is adjacent to and at leastpartially overlies the front surface, the plate having a plurality ofscrew holes for receiving the shafts of the screws, the screw holesextending through the plate and having a central axis, at least twoscrew holes extending through the plate at an angle such that thecentral axis of the screw hole ranges from about 25° to about 70° withrespect to the horizontal center plane or a plane parallel to thehorizontal center plane.
 2. The system of claim 1, wherein the threedimensional body has a plurality of boreholes, the boreholes extendingfrom the front surface to at least one of the upper surface and thelower surface.
 3. The system of claim 2 , wherein, when the plate iscoupled to the three-dimensional body, the three-dimensional body and atleast one of the angled screw holes in the front plate is configured andoriented such that one of the screws inserted into that angled screwhole pierces at least partially at least one of the upper surface andthe lower surface of the three-dimensional body.
 4. The system of claim1, wherein, when the front plate is secured to the three-dimensionalbody, the central axis of at least one of the angled screw holes extendstoward the upper surface of the three-dimensional body and the axis ofat least one of the angled screw holes extends toward the lower surfaceof the three-dimensional body.
 5. The system of claim 1, wherein thethree-dimensional body is made from a non-metallic material.
 6. Thesystem of claim 5, wherein the front plate is formed of a metallicmaterial.
 7. The system of claim 1 wherein the front plate has asuperior surface and an inferior surface and a height between thesuperior surface and the inferior surface and wherein the front surfaceof the three-dimensional body has a height between the upper surface andlower surface that is substantially equal to the height of the frontplate.
 8. The system of claim 1, wherein the first plate has a superiorsurface and an inferior surface and a height between the superiorsurface and the inferior surface and the three-dimensional body has aheight between the upper surface and lower surface, wherein the maximumheight of the three-dimensional body is substantially equal to orgreater than the height of the front plate.
 9. The system of claim 1,wherein the three-dimensional body further includes at least oneborehole in communication with the front surface and one of the uppersurface or the lower surface and the front plate is couplable with thethree dimensional body so that at least one of the angled screw holesformed in the front plate aligns with the at least one borehole in thethree-dimensional body so that one of the bone screws is insertablethrough the angled screw hole formed in the plate, through the recessformed in the three dimensional bodies and into one of the vertebrae.10. The system of claim 1, wherein the three dimensional body includesat least one through hole extending from the upper surface to the lowersurface.
 11. The system of claim 1, wherein at least one of the angledscrew holes formed in the front plate is conically shaped such that ittapers conically towards the front plate's bottom surface.
 12. Thesystem of claim 1, wherein one of the angled screw holes in the frontplate includes internal threads, and at least a portion of the head ofone of the bone screws has external threads for engaging the internalthread of the angled screw hole.
 13. The system of claim 1, wherein atleast one the angled screw holes in the front plate has internal threadsand that threaded portion is conically tapered and wherein a pluralityof the bone screws have at least a portion of their heads externallythreaded.
 14. The system of claim 1, wherein one of the upper and lowersurfaces of the three dimensional body is convex.
 15. The system ofclaim 1, wherein the front plate has a plurality of angular screw holesand the three-dimensional body has a plurality of boreholes foralignment with the angular screw holes wherein the angular screw holeswhen aligned with the boreholes form passages for the screws thatdiverge as the passages extend away from the front surface into thethree-dimensional body.
 16. The system of claim 1, wherein the frontplate has a plurality of angular screw holes and the three-dimensionalbody has a plurality of boreholes for alignment with the angular screwholes, wherein the angular screw holes when aligned with the boreholesform passages for the screws that are parallel as they extend away fromthe front surface into the three-dimensional body.
 17. The system ofclaim 1, wherein the three dimensional body further has a convex leftside surface, a convex right side surface and a back surface.
 18. Thesystem of claim 2, wherein the three-dimensional body further includes aleft-side surface, a convex right side surface and a back surface, andthe three-dimensional body does not have boreholes to receive screwsthat pass through either the left side or the right side.
 19. The systemof claim 1, wherein the three-dimensional body has angular boreholesthat extend from the front face to at least one of the upper surface andthe lower surface and the boreholes do not cross the horizontal plane.20. A spine stabilizing system for stabilizing first and secondvertebrae in a spinal column comprising: a plurality of bone screwshaving a threaded shaft and a head, the shaft having a longitudinalcentral axis; a three dimensional body formed of plastic configured forinsertion between endplates of the first and second vertebrae, the threedimensional body having an upper surface for abutting the endplate of afirst vertebrae, a lower surface for abutting the endplate of a secondvertebrae, a front surface, and a horizontal center plane between theupper and lower surface; and a front plate formed of a metallic materialhaving a top surface, a bottom surface, a superior surface and aninferior surface, the plate couplable to the three dimensional body suchthat the bottom surface overlies the front surface, the plate having aplurality of screw holes for receiving there through the shaft of thescrews, the screw holes having a central axis and extending through theplate at an angle such that the central axis of the screw hole rangesfrom about 25° to about 70° with respect to the horizontal center planeor a plane parallel to the horizontal center plane, wherein a firstangled screw hole is angled in the front plate toward the superiorsurface of the front plate and the second angled screw hole is angled inthe front plate toward the inferior surface of the front plate.
 21. Thesystem of claim 20, wherein at least one of the angled screw holesincludes internal threads.
 22. The system of claim 20, wherein at leastone of the screws includes external threading at least partially on itshead.
 23. The system of claim 20, wherein the height of the front plateis substantially equal to the height of the front surface of thethree-dimensional body.
 24. The system of claim 20, wherein the threedimensional body has a horizontal middle plane between the upper surfaceand the lower surface, and the front plate is coupleable to the threedimensional body such that the axis of at least two angled screw holesdefine an angle ranging from about 25° to about 70° with the horizontalmiddle plane.
 25. A spine stabilizing system for stabilizing first andsecond vertebrae in a spinal column comprising: a plurality of bonescrews having a threaded shaft and a head, the shaft having alongitudinal central axis; a three dimensional body configured forinsertion between endplates of the first and second vertebrae, the threedimensional body having an upper surface for abutting the endplate of afirst vertebrae, a lower surface for abutting the endplate of a secondvertebrae, a left side surface and a right side surface, a front surfaceand a back surface, the three dimensional body having a horizontalcentral plane between the upper and lower surface, the three-dimensionalbody having a plurality of boreholes for receiving there through thescrews, at least one borehole extending from the front surface to theupper surface of the three dimensional body and at least one boreholeextending from the front surface to the lower surface of the threedimensional body, each borehole having a central axis wherein eachcentral axis is at an angle in the range of about 25° to about 70°relative to the horizontal middle plane of the body.
 26. The system ofclaim 25, wherein the plurality of bore holes are aligned in the frontsurface in a horizontal line.
 27. The system of claim 25, furthercomprising: a front plate having a top surface, a bottom surface, asuperior surface and an inferior surface, the plate couplable to thethree dimensional body such that the bottom surface overlies the frontsurface, the plate having a plurality of screw holes for receiving therethrough the shaft of the screws, the screw holes having a central axis,at least two of the plurality of screw holes extending through the frontplate so that the axis of the screw hole is at an angle that issubstantially equal to the angle of the boreholes in thethree-dimensional body, wherein the position and orientation of thefront plate is such that the at least two angled boreholes in the threedimensional body are aligned with the at least two angled screw holes inthe front plate so that the screws are insertable in the front plate sothat its shaft extends out of respective upper and lower surfaces of thethree-dimensional body.
 28. The system of claim 27, wherein when theplate is coupled to the three-dimensional body, the three-dimensionalbody and at least one of the screw holes in the front plate areconfigured and oriented such that one of the screws inserted into theangled screw hole pierces at least partially one of the upper or lowersurfaces of the three-dimensional body.
 29. The system of claim 25,wherein the three dimensional body is formed of a non-metallic material.30. The system of claim 25, wherein the three dimensional body includesat least one through hole extending from the upper surface to the lowersurface.
 31. The system of claim 27, wherein at least one of the angledscrew holes formed in the front plate is conically shaped.
 32. Thesystem of claim 25, wherein one of the upper and lower surfaces of thethree dimensional body is convex.
 33. The system of claim 25, wherein atleast one of the upper surface and the lower surface includes one of thegroup of grooves, ribs, teeth and roughened surface portion to improveanchoring of the three-dimensional body with the vertebrae.